Adjustable centrifugal switch



July 18, 1950 Q. J. EVANS ETAL ADJUSTABLE CENTRIFUGAL SWITCH Filed Sept. 26, 1947 Fig.3.

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INVENTGR. QUENTQN J. EVANS EV ALBERT KUSHNER Patented July 18, 1950 UNITED STATES PATENT OFFICE ADJUSTABLE CENTRIFUGAL SWITCH Quentin J. Evans, New York, N. Y., and Albert Kushner, Oak Ridge, Tenn., assignors to the United States of America as represented by the United States Atomic Energy Commission Application September 26, 1947, Serial No. 776,310

4 Claims.

.This invention relates to electrical switches and, more particularly, to an improved electrical switch responsive to the speed of rotation of a shaft to open and close a circuit at predetermined speeds of rotation.

Power-driven shafts are often run in conjunction with auxiliary devices which it is desirable to activate or to inactivate at some definite speed of rotation of the shaft. Such devices as motorgenerator pairs are often used with auxiliary devices, such as booster generators. When such an auxiliary device is used it is often desirable that apparatus be available automatically and precisely to inactivate or activate the devices at definite values of the speed of rotation of the shaft.

Accordingly, it is an object of this invention to provide an adjustable switch responsive to the speed of rotation of the shaft.

It is another object of the invention to provide an improved centrifugal switch of relatively simple construction and capable of fine adjustment over a wide range of speeds.

It is another object of the invention to provide a device for activating and inactivating an auxiliary electrical circuit at predetermined speeds of rotation of a power-driven shaft.

Other objects, advantages, and modifications of the invention will become obvious in the following description.

To accomplish the foregoing objects a preferred embodiment of the present invention is presented in which there is provided a pair of annular conductor rings mounted on an insulating plate rotatable with a shaft, a stationary contact mounted on the insulating plate and operably connected to one of the conductor rings and a second adjustable contact radially movable with respect to the stationary contact and operably connected to the second conductor ring. The conductor rings are insulated from each other so that radial movement of the second contact against the action of a spring determines the continuity of the connection between the conductor rings. Then, by placing the conductor rings in an electrical circuit by means of suitable contact brushes the electrical circuit is open or closed depending upon the position of the radially movable contact.

Several types of centrifugal switches are known but these are generally fabricated so that they open at some definite speed of rotation for which the switches are set at the time of manufacture. In order to adjust the speed of rotation at which such a switch operates, it is often necessary to make a major change in the switch such as replacing the springs with springs of a different resiliency. The present invention provides two simple adjustments which may be made with relatively little difficulty to change the speed of rotation at which the switch will'open. A relatively coarse adjustment is obtained by altering the tension or compression on the spring which resists the movement of the radially movable contact. A second and finer adjustment is made by changing the weight distribution of the movable contact. Since the centrifugal force exerted by the movable contact when the switch rotates varies with the distance between the center of gravity of the contact and the axis of rotation, a change in the weight distribution of the movable contact will cause a corresponding change in the position of the center of gravity of the contact and thus in the effective radius. Accordingly, an adjustment in the weight distribution of the movable contact will result in a corresponding change in the speed of rotation at which the movable contact exerts a sufficiently great centrifugal force to overcome the thrust of the restraining spring. The simplicity and fineness of this adjustment over a wide range of speeds result in extremely accurate control over the operation of the centrifugal switch. Thus by first adjusting the tension or compression of the spring and then by adjustment of the weight distribution of the movable contact the centrifugal switch may be made to operate at a predetermined speed of rotation with a high degree of precision.

The invention will be described with reference to a specific embodiment and it is to be understood that the invention is not limited thereto.

In the accompanying drawing, Figures 1, 2 and 3 show an embodiment of the switch adapted for opening when the desired speed of rotation is reached, and Figure 4 shows an embodiment of the switch adapted for closing upon reaching a desired speed of rotation.

Figure 1 is a front elevation of the centrifugal switch mounted on a shaft and shows the positions of the stationary contacts and the movable, adjustable contacts on one face of the insulating plate.

Figure 2 is a rear elevation of the centrifugal switch showing the relative positions of the conductor rings mounted on the insulating plate and, diagrammatically, a method of establishing contact between the circuit to be controlled and the conductor rings.

Figure 3 is a cross-sectional view of the centrifugal switch taken on the line 3-3 of Figure 1.

Figure 4 is a cross-sectional view through the contacts of an embodiment of the centrifugal switch adapted to close at a predetermined speed of rotation.

Referring first to Figures 1, 2 and 3, rigidly positioned on the rotatable shaft l2 by means of the set screws I3 is the collar having a flanged portion 3|. n the flanged portion 2| of the collar an insulating plate It is rigidly mounted by means of the screws 22. The insulating plate In is generally circular and may be made of such material as Bakelite or other similar insulating material. Secured to the back side of the insulator plate are flat, concentric annular conductor rings l4 and I! of brass or similar conducting material. Conductor rings M and I5 are secured to the insulating plate ID by means of screws 25 and |6 respectively, and are spaced for insulation from each other and from the shaft l2. The rings are centered on the axis of rotation. Suitable contact brushes l8 and I9 (shown diagrammatically) bear against rings H and |5 respectively so that the electrical circuit to be controlled may be connected across the conductor rings l4 and I5. The surfaces of conductor rings H and I5, against which the brush contacts bear, are generally smooth so that there is a minimum of interference with the rotation of the shaft.

Reference will be made now to Figures 1 and 3 and particularly to the latter to describe the make-and-break elements of the switch mechanism. 0n insulating plate ID are mounted two substantially identical make-and-break elements on directly opposite sides of the shaft |2 so that the switch is balanced whenrotating. One of the make-and-break elements will be described, and this description will apply equally to the other element.

On the face of the insulating plate opposite the conductor rings is mounted the bracket by means of the screws which serveas electrical connection between bracket 20 and conductor'ring It. The bracket 20 carries a radially movable threaded conductor pin 2| that extends thr ugh bracket guide holes 22 which are large enough to allow the conductor pin to move freely toward and away from the axis of rotation of the shaft. Surrounding the pin 2|, between the inner and remote bracket arms 36 and 34 respectively is the helical spring 23 that bears at its outer end against the outer bracket arm 3 and at its inner end against tensioning nut 24 which is threaded onto pin 2|. The tensioning nut 24 is threaded on the conductor pin so that the position of the tensioning nut can be changed to adjust the compression of the spring 22 and thus to provide a relatively coarse adjustment of the speed of rotation of the shaft at which pin 2| moves radially against the spring.

Extending from the inner conductor ring IS through insulating plate It and outward in the same plane as movable pin 2|, is stationary conductor pin, or contact, 26. To complete the connection between conductor rings H and IS, the movable conductor pin 2| bears against the stationary conductor pin 26 when the centrifugal force on the movable pin is insufllcient to overcome the action of spring 23.

A nut 30 is threaded on the end of the movable pin 2| between the inward bracket arm 25 and the conductor pin 26 to restrict the radial movement of pin 2|.

0n movable pin 2| is a threaded weight 21 which may be moved to any position on the movable pin outside bracket arm 24 to adjust the distribution of weight of the movable contact. This provides a relatively fine adjustment of the switch to determine the speed of rotation at which the movable contact has sufficient centrifugal force to move radially outward and break the connection with the stationary contact. That is, the further the weight 21 is from the axis of rotation, the smaller is the centrifugal force necessary to move the pin 2|, and the lower the speed of rotation at which the switch opens. when the ,shaft and switch are at rest, the movable conductor pins 2| are in contact with the stationary conductor pins 26 and the switch is then closed so that there is a completed circuit from the external circuit through one of the concentric conductor rings, the movable and stationary contacts, and thence through the second concentric conductor ring. The positions of the tensioning nuts 24 and the threaded weights 21 are adjusted so that the movable conductor pins 2! will move radially away from the stationary pins 26 against the thrust of the springs 23 at a predetermined speed of rotation to break the electrical circuit. The circuit remains closed until the redetermined speed is reached, that is, until the centrifugal force on the movable pins 2| is suflicient to overcome the thrust of the springs 23. The switch will remain open at all speeds above that for which it has been priorly set.

In a similar manner, when the shaft is coming to rest the switch again closes when the shaft has slowed to the predetermined speed thus re-closing the circuit. a By interchanging the positions of the movable and stationary pins and their electrical connections to the conductor rings as shown in Figure 4, the switch may be used to close an external electrical circuit at some desired speed of rotation. In this case the brackets 20 bearing the movable pins 2| are electrically connected to the inner conductor ring I5 while the stationary contacts 25 are electrically connected to the outer conductor ring I4. The helical springs as bear against the remote bracket arms 34 so that when the shaft is at rest the thrust of the helical springs 23 tends to keep the movable pins 2| from moving outward toward the periphery of the switch. The threaded weights 21 may then be in a position between bracket arms 35 and the inner ends of movable pins 2| or in some other suitable position on the pins 2|. Thus when the shaft is in rotation the force on the movable pins 2| increases as the speed of rotation is increased .5 until it is sufficient to overcome the thrust of the springs 23. Pins 2| then move toward the periphery of the switch to make contact with the stationary contact pins 26 to close the circuit. Contrariw-ise whenthe speed of the shaft 00 is decreased and thus the-force on the movable pins is decreased. the switch opens when the predetermined speed is reached.

The switch as described herein may be adapted for controlling a sumber of electrical circuits all I of whose operation it is desirable to control in accordance with the speed of rotation of a powerdriven shaft. This may be accomplished by mounting on the insulating plate a suitable number of conductor rings with appropriate contact 10 members. Since the movable contacts may be adjusted to open and/or close at any desired speeds of rotation, it is possible to operate a number of circuitseach at a different speed of rotation. 1| The centrifugal switch as described hereinbefore is capable of many uses. For example, it may be used through a relay on the power supply to an induction motor which is used for starting a synchronous motor. The switch shown in the accompanying diagrams has been operated at a range of speeds from about 200 to 5000 revolutions per minute by simple adjustment of the tension on the springs and the positions of the threaded weights.

Other alternatives will be apparent to those skilled in the art.

Since many embodiments might be made of the present invention and since many changes might be made in the embodiment described, it is to be understood that the'foregoing description is to be interpreted as illustrative only and not in a limiting sense.

We claim:

1. An electrical switch responsive to the speed of rotation of a shaft which comprises a contact element rotatable in fixed relation to said shaft, a contact comprising an elongated threaded pin rotatable with said shaft and radially movable with respect to said contact element, spring means for resisting radial movement of said radially movable contact, a tension adjusting nut threaded on said pin for regulating the radial thrust of said spring means, said spring means bearing against said tension adjusting nut to urge said radially movable contact toward said contact element, means for regulating the weight distribution of said radially movable contact comprising a weight threaded on said pin and two concentric conductor rings in spaced relationship to one another for insulation, one of said conductor rings being electrically connected to said movable contact and the other of said conductor rings being electrically connected to said contact element, said tension adjusting nut and said weight regulating means being adapted to determine the speed of rotation at which said movable contact has sufiicient centrifugal force to overcome the radial thrust of said spring.

2. An electrical switch responsive to the speed of rotation of a shaft which comprises an insulating plate mounted to rotate with said shaft, 9. pair of concentric annular conductor rings spaced from each other for insulation and mounted on one side of said plate for rotation therewith, a contact element on the other side of said plate in fixed relation to said shaft and electrical- 1y connected to the inner of said conductor rings, a conducting bracket having an inner and an outer arm and mounted on the side of said plate opposite said conductor rings and electrically connected to the outer ring, a threaded elongated contact pin in slidable contact with the arms of said bracket, an adjusting nut threaded on said pin between said bracket arms, a spring 'in compression between said adjusting nut and said outer bracket arm urging the contact pin toward said contact element, the position of said nut regulating the radial thrust of said spring, and a threaded weight on said pin for adjusting the position of the center oi gravity of said contact pin whereby adjustment of said adjusting nut and said threaded weight determine the speed of rotation of said shaft at which the contact pin breaks contact with the contact element.

3. Electrical switch apparatus responsive to the speed of rotation of a shaft which comprises an insulating plate mounted to rotate with said shaft, a pair of concentric annular conductor rings spaced from each other for insulation and mounted to rotate with said insulating plate and a pair of switching elements spaced on opposite sides of said shaft, each switching element comprising a contact element rotatable in fixed relation to said shaft and electrically connected to one of said conductor rings, an elongated threaded contact pin rotatable with said shaft and radially movable with respect to said contact element, said pin being electrically connected to the other of said conductor rings, a nut threaded on said pin, a spring bearing against said nut to urge said pin toward said contact element, the thrust of said spring being determined by the position of said nut, and a threaded weight on said pin for adjusting the position of the center of gravity of said pin.

4. An electrical switch responsive to the speed of rotation of a shaft which comprises an insulating plate mounted to rotate with said shaft, a pair of annular conductor rings spaced from each other for insulation and mounted to rotate with said insulating plate, a contact element rotatable in fixed relation to said shaft and electrically connected to one of said conductor rings, a contact comprising an elongated threaded pin rotatable with said shaft and radially movable with respect to said contact element, said contact being electrically connected to the other of said conductor rings, a spring for resisting radial movement of said radially movable contact, a tension adjusting nut threaded on said radially movable contact for regulating the radial thrust of said spring, said spring bearing against said tension adjusting nut to urge said radially movable contact toward said contact element, and a threaded weight on said pin for adjusting the position of the center of gravity of said movable contact.

QUENTIN J. EVANS. ALBERT KUSHNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,338,041 Rohman Apr. 27, 1920 1,645,556 Von Arco Oct. 18, 1927 1,855,703 Cloud Apr. 26, 1932 FOREIGN PATENTS Number Country Date 18,869 Great Britain Apr. 27, 1911 856,316 Germany Feb. 3, 1938 

